One of heat-processing apparatuses used in a semiconductor manufacturing process is a vertical heat-processing apparatus which is a heat-processing apparatus of a batch type. In the vertical heat-processing apparatus, a heating furnace is composed of a vertical reaction tube whose lower end is opened, and a heater surrounding an outside of the reaction tube. A wafer holder called “wafer boat” holding a plurality of semiconductor wafers (referred to as “wafer” herebelow) in a tier-like manner is loaded from the lower side of the reaction tube, and the heating furnace is hermetically sealed. Then, the wafers are subjected to a heat process. As the heat process, there are conducted an oxidation process, a diffusion process, a film-deposition process by a CVD, and so on.
Components of a heat-processing apparatus, such as a reaction tube, a wafer boat, and a heat-insulation unit (heat-retention unit), are generally made of quartz. These quartz products are obtained by subjecting a quartz ingot to various machining processes. During these machining processes, a metal contamination such as a copper contamination may occur because of contact between the quartz product and a machining tool or an influence of a working atmosphere. Since the quartz product is cleaned with a hydrofluoric acid by a manufacturing company (maker) of the quartz product, the copper on a surface of the quartz product will be removed in theory. However, in actual practice, since copper is difficult to be ionized, the copper dissolved in the hydrofluoric acid may again adhere to the surface of the product. As a result, there is a possibility that a slight amount of copper remains on the surface of the quartz product.
Quartz products delivered to a manufacturing company (maker) of a semiconductor device are assembled into a vertical heat-processing apparatus which is then delivered to a user. When a surface of the quartz product is contaminated with copper, although slightly, the following problem may take place. That is to say, when the user starts an operation of the apparatus to heat-process a wafer, the copper on the surface of the quartz product is heated to activate a molecular motion of the copper. Thus, some molecules are scattered in the heat-processing atmosphere, and adhere to the wafer to contaminate the same. In recent years, due to a thinner film and further miniaturization of a semiconductor device, the wafer contaminated with copper, although slightly, may affect electric properties of the semiconductor device to degrade throughput thereof.
On the other hand, JP2002-313787A (especially, claim 1, sections 0017 and 0027) describes that, after quartz products are assembled into a heat-processing apparatus and before an oxidation process starts, the quartz products are baked by a hydrogen chloride gas and an oxygen gas. However, this method is disadvantageous in that it takes a long time before an operation of the apparatus starts.
JP2002-313787A also describes that the quartz products are baked (subjected to a baking process) before the quartz products are assembled into a heat-processing apparatus. This process, i.e., baking the quartz products beforehand, is practically advantageous in reducing a time required for the user to start an operation of the apparatus. In this case, it is preferable that the quartz products of the vertical heat-processing apparatus, such as a reaction tube, a wafer boat, an insulation unit below the wafer boat, and a temperature sensor unit, are efficiently, uniformly baked by a user-friendly baking method. However, no concrete manner of the baking process is described in JP2002-313787A.